as a phpBB3 administrator myself, I recommend you to replace the CAPTCHA anti-spam module that's currently in use with the "Q&A" plugin that comes installed with the board. In that plugin, you can define some custom questions and acceptable answers, which will make it impossible for spambots to register on the site, as you can ask questions related to the forums, NecroDancer or otherwise.

For example, if the question is "Please fill in the name of our company: 'Brace [...] Games'", and the answer is "Yourself", it's going to be tough for a spambot to process that.

On my Unreal fansite, I used a question like "What is the name of the classic videogame this site is about?". You may want to make your question(s) simpler, to make it easier for foreign players to register.

CAPTCHA modules are circumvented frequently; Q&A not so much. Try it out!

The Q&A plugin can be configured in the ACP -> General -> Spambot Countermeasures.

No, it's a Recapctha at the moment. But this already got addressed on Twitter; the forums had Q&A registration before, and it didn't help either. There's humans at work cracking those security measures, so little can help.